BACILLUS COLL 455 



MORPHOLOGY. In shape it is a rod with rounded 

 ends, sometimes so short as to appear almost spherical, 

 while again it is seen as very much longer threads. 

 Often both forms are associated in the same culture. 

 It may occur as single cells, or as pairs joined end to 

 end. 



It has no peculiar morphological features that can 

 aid in its identification, for in this respect it simu- 

 lates many other organisms. It is usually said to be 

 motile, and undoubtedly is motile in the majority of 

 cases ; but its movements are at time so sluggish that a 

 positive opinion is often difficult. 



By Loffler's method of staining, flagella can be de- 

 monstrated, though usually not in such numbers as are 

 seen to occur on the typhoid fever bacillus. 



It does not form spores. 



It grows both with and without free oxygen. 



Ox GELATIN. On the surface its colonies appear as 

 small, dry, irregular, flat, blue- white points that are 

 commonly somewhat dentated or notched at the margin. 

 They are a trifle denser at the centre than at the 

 periphery, and are often marked at or near the middle 

 by an oval or round nucleus-like mass the original 

 colony from which the layer on the surface developed. 

 When located in the depths of the gelatin, and ex- 

 amined with a low-power lens, they are at first seen to 

 be finely granular and of a very pale greenish-yellow 

 color; later they become denser, darker, and much 

 more markedly granular; in shape they are round, 

 oval, and lozenge-like. AVhen the surface colonies are 

 viewed under a low power of the microscope they pre- 

 sent essentially the same appearance as that given for 

 the colonies of the bacillus of typhoid fever, viz., they 



